1. Field of the Invention
The present invention generally relates to a lithography apparatus and method, and more particularly to a method and apparatus for direct mechanical referencing of a surface (e.g., a top surface) of a workpiece during in nano-imprint lithography.
2. Description of the Related Art
Conventional imprint lithographic methods rely on extremely precise translation stages and fixtures to locate a workpiece or substrate under the imprint template (e.g., mold or mask) such that the template is exactly parallel to the workpiece. Typically, in nano-imprint techniques, a rigid quartz template (also referred to as a mask or mold) is employed in which features have been etched. A liquid photoresist is deposited on a workpiece (e.g., usually a semiconductor wafer), and the quartz mask is pressed against the liquid resist, which fills the cavities in the mask and spreads out between the mold and the wafer. The photoresist is then exposed to ultraviolet (UV) radiation causing it to polymerize, and the mask is pulled off. What is left on the polymerized resist-coated surface of the workpiece are the inverted topographical features of the mask.
In order to achieve practical results, several precision steps must be performed. First, the mask must be precisely positioned over and parallel to the resist-coated workpiece. The mask is then lowered and laterally aligned to the features on the workpiece while maintaining precise parallelism. As this is performed, appropriate normal and lateral steering forces are applied as the photoresist spreads out under the mask such that the resist spreads out evenly. Precise optical alignment of features on the mask relative to those on the workpiece is performed as this process occurs. Finally, when the resist has been sufficiently spread out and aligned, the resist is exposed and polymerized using ultraviolet light and the mask is removed.
Thus, in order to achieve the strict precision required, conventional positioning stages are employed. These conventional stages are large, expensive and slow. Thus, efficiency, costs and throughput are compromised.
Hence, prior to the present invention, there has been no method or system for rapidly and precisely registering the workpiece in the Z-dimension relative to the imprint mold. Moreover, the conventional systems and method have not achieved a precise parallelism between mask and workpiece using an air bearing design.